Determining the geographic location of a portable electronic device

ABSTRACT

Determining the geographic location of a portable electronic device ( 100 ) in a radio communications network, by transmitting radio signals from a plurality of first network transmitters ( 200, 300, 400 ); receiving, in the network, a measurement signal from the portable electronic device, which measurement signal comprises, for each transmitted radio signal, a plurality of data samples obtained in the electronic device from the respective transmitted signal at different time points during a measurement period with movement of the portable electronic device ( 100 ), and local position data associated to each data sample obtained from a local positioning unit in the electronic device, so as to form a synthetic antenna array; obtaining, a direction measurement between the electronic device and the first network transmitter from the synthetic antenna array; obtaining geographic location data for the first network transmitter; and identifying geographic location data of the portable electronic device based on the direction measurement and the geographic location data for the first network transmitter.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of International ApplicationNo. PCT/EP2014/074024, filed Nov. 7, 2014, the disclosure of which ishereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a technique for determining thegeographic location of a portable electronic device, and in particular atechnique that can be used as an alternative or supplement to well-knownGNSSs (Global Navigation Satellite Systems) or an improvement to 3GPPtriangulation.

BACKGROUND

Satellite navigation systems provide autonomous geo-spatial positioningwith global or regional coverage. At the present, the dominating GNSS isthe Global Positioning System (GPS). A GPS receiver has the ability todetermine its geographic location (longitude, latitude, and altitude) towithin a few meters using time signals transmitted along a line-of-sightby radio from satellites.

However, there are situations when it is not possible or even permittedfor a portable electronic device with a GPS receiver to receive thesatellite signals used for positioning. For example, satellite signalsmight be obscured or blocked when the handheld device is operatedindoors, or in difficult urban areas with sky rises blocking thesatellite signal. Still further, the GPS system might have inadequatecoverage in a specific geographic area, or the satellite signals may beactively jammed to prevent positioning.

Furthermore, it may be desirable to have the option of providingpositioning functionality to a portable electronic device without theneed to incorporate a GPS receiver, which adds cost, space and energyconsumption to the portable electronic device.

It is well-known that antenna arrays with several physical antennaelements (denoted “physical antenna arrays” in the following) can beused for directional estimation of incoming signals. A portableelectronic device with a physical antenna array is e.g. disclosed inUS2008/0100502. The portable electronic device estimates the directionof arrival of incoming radio signals when located at two differentpositions, by processing the incoming radio signals received from asignal source by the plural antenna elements at the first and the secondposition, respectively. Further, a built-in motion detector indicatesthe displacement vector between the first and second positions. Thedisplacement vector in combination with the directions allows theportable electronic device to be positioned relative to the signalsource.

One problem with physical antenna arrays is that they are large andbulky and usually consume more space than a portable electric device canafford. They may also require precise calibration, so that the responseof each antenna element is known in all possible directions, in order toenable directional estimation.

In the field of antennas, there are also so-called virtual or syntheticantenna arrays which make use of robots to move a single physicalantenna element to a number of known positions. The signals recorded atthe different positions can be processed just as data from physicalantenna arrays, as long as the surroundings of the antenna aresufficiently static during the measurement, and can therefore also beused for directional estimation. Like physical antenna arrays, virtualantenna arrays are bulky, mainly due to the need for a positioningdevice (usually some kind of robot or rail). Virtual antenna arrays aregenerally not developed with size constraints in mind, but are ratherused to avoid the requirement for (the often cumbersome) calibration orto avoid coupling effects that may arise between the plural antennaelements of a physical antenna array, see e.g. L. M. Correia: Mobilebroadband multimedia networks, Academic press (2006) chapter 6.6.Virtual antenna arrays of this type are thus unsuitable for use inportable electronic devices.

The prior art also comprises an article by Broumandan et al: “Directionof arrival estimation of GNSS signals based on synthetic antennaarrays”, ION GNSS 2007, 25-28 Sep. 2007, pages 1-11. Broumandandiscloses a technique for enhancing GNSS accuracy in urban environments,to reduce the influence of interfering signals generated by reflectionsof the incoming signals on buildings and other scattering objects inurban environments. This is achieved by determining the directions ofthe interfering signals and applying adaptive antenna algorithms todesign a beamformer to place nulls in the directions of the interferingsignals, thereby improving the signal quality of the GNSS signals usedfor global positioning. Broumandan proposes that an antenna array issynthesized by moving a handheld device with a single antenna in anarbitrary direction while continuously sampling the interference signal.The trajectory of the single array is determined by an inertialmeasurement unit (IMU) in the handheld device. The resulting set ofspatial samples together with the trajectory form a synthetic antennaarray, which can be processed for determining the direction of arrivalfor each interfering signal.

The prior art further comprises DE102006037247, which focuses on solvinga multi-path problem in connection with time-of-arrival (TOA) orroundtrip-time-of-flight (TOF) positioning techniques, including GPS.The TOA and TOF techniques are based on obtaining measurement signalsthat represent the amplitude and phase of a transferred signal dependenton the transit time between a mobile station and each of a plurality ofstationary stations. The measurement signals are used for calculatingthe distance to each stationary station based on the transit times inthe same way as for conventional radar systems, see e.g. Merrill IvanSkolnik: Introduction to Radar Systems, McGraw-Hill (2002), Chapter 1.1.The multi-path problem arises when signal reflections generate furthersignal paths in addition to the direct signal transmission path betweenthe mobile station and the stationary station. DE102006037247 suggestssolving this problem by generating a synthetic aperture which isdesigned to form a directionally exact antenna, so as to increasesignal-to-noise and reduce the influence of signal reflections on thetransit time estimates. It is well known that the resolution of anestimated transmit time is inversely proportional to the bandwidth ofthe signal; therefore the positioning in DE102006037247 requires abroadband radio signal to get adequate estimates of transit time.Furthermore, the positioning in DE102006037247 requires synchronizationacross all the stationary stations, or synchronization between themobile station and each of the stationary stations.

Another type of single antenna direction-finding system is known fromU.S. Pat. No. 5,502,450. Here, a single antenna is arranged on anaircraft to receive a signal from a source while the aircraft movesalong a linear flight path. A system connected to the antenna detectsperiodically occurring symbols in the signal at two positions along theflight path and calculates, based on the corresponding signal transmittime, the distance to the source at each position. The distance betweenthe positions along the flight path is determined using existingnavigational means. Based on these distances and applying trigonometrycalculations, the system is able to estimate the angle or the distanceto the source at a downstream position along the linear flight path.

WO2011146011 A1 presented a self-positioning portable electronic device,which also need only one antenna element. In the proposed method, theelectronic device receives a signal from one or more remotetransmitters, and a local positioning unit determines a local positionof the device. The device operates to obtain a plurality of data samplesfrom the signal at different time points during a measurement periodwith movement of the portable electronic device along an arbitrarytrajectory, associate each data sample with a local position obtainedfrom the local positioning unit so as to form a synthetic antenna array,obtain an array response of the synthetic antenna array, and identifythe geographic location of the portable electronic device, by processingthe synthetic antenna array as a function of the array response andusing knowledge about the geographic location of the transmitter. Theuse of the array response allows the geographic location to beidentified independently of signal transit time between the transmitterand the device.

SUMMARY

It is an object of the invention to at least partly overcome one or moreof the limitations of the prior art.

In view of the foregoing, one object is to provide a new positioningtechnique which is suitable from a resource point of view, forpositioning of portable electronic devices, i.e. a technique fordetermining the geographic location of such portable electronic devices,as an alternative or supplement to the use of conventional GNSS or animprovement to 3GPP triangulation.

One or more of these objects, and further objects that may appear fromthe description below, are at least partly achieved by means of amethod, a computer program product, a computer-readable medium andportable electronic devices according to the independent claims,embodiments thereof being defined by the dependent claims.

A first aspect of the invention is a method of determining thegeographic location of a portable electronic device in a radiocommunications network. The method comprises the steps of: transmittingradio signals from a plurality of first network transmitters; receiving,in the network, a measurement signal from the portable electronicdevice, which measurement signal comprises, for each transmitted radiosignal, a plurality of data samples obtained in the electronic devicefrom the respective transmitted signal at different time points during ameasurement period with movement of the portable electronic device, andlocal position data associated to each data sample obtained from a localpositioning unit in the electronic device, so as to form a syntheticantenna array; obtaining, in the network, a direction measurementbetween the electronic device and the first network transmitter from thesynthetic antenna array; obtaining geographic location data for thefirst network transmitter; and identifying geographic location data ofthe portable electronic device based on the direction measurement andthe geographic location data for the first network transmitter

The first aspect is based on performing the geographic positioning ofthe portable electronic device based on a directional estimationobtained by means of the synthetic antenna array. In one embodiment,e.g. by processing the synthetic antenna array as a function of thearray response, the geographic location may be identified independentlyof signal transit time between transmitter and the portable electronicdevice. As noted above, although prior art techniques combine TOA or TOFtechniques with a synthetic antenna array, this is not done forpositioning, but for shaping and directing a synthetic aperture eithertowards transmitters to improve signal quality or to determinedirections of interfering signals. In other words, in the prior art, thesynthetic antenna array is used for obtaining data samples, whereas theinventive method uses the synthetic antenna array when processing thedata samples for identifying the geographic location, specifically byprocessing the synthetic antenna array as a function of the arrayresponse. The array response may be seen as a model of the signalresponse at the local positions, in terms of at least the phase of thesignal, and possibly also the amplitude of the signal, as a function ofthe relative location between the synthetic antenna array and thetransmitter, while neglecting any differences in time delay between thelocal positions with respect to the transmitter.

In addition, the first aspect is based, on the one hand, on datacollection in the electronic device, and on the other hand, calculationmade in the network. This minimizes the processing and storagerequirements of the portable electronic device, and provides an improvedinterface for other stakeholders, such as rescue services.

In one embodiment, the method is combined with receiving time differencedata from the portable electronic device, representing time differencemeasured between specific signals from at least a number of secondnetwork transmitters; wherein the step of identifying the geographiclocation includes the step of combining a direction measurement betweenthe electronic device and at least one of the first networktransmitters, established from said array response, with said timedifference data. In such an embodiment, the positioning bases on thesynthetic array may thus be combined with e.g. an OTDOA (Observed TimeDifference Of Arrival), a positioning feature introduced in 3GPP rel9 ofE-UTRA, LTE.

In one embodiment, the steps of receiving a measurement signal andreceiving time difference data are carried out independently from eachother. These measurements may however still be carried out on the samesignals, such as on PRS (Positioning Reference Signal), transmitted bybase stations of a cellular LTE system.

In one embodiment, the steps of identifying the geographic locationcomprises the step of correlating geographic location informationobtained from processing the synthetic antenna array, with geographiclocation information determined from said time difference data. In suchan embodiment, an improved positioning accuracy may be obtained,compared to using only e.g. OTDOA.

In one embodiment, the first network transmitters are wireless accesspoints, and the second network transmitters are cellular base stations.Alternatively, both the first and the second network transmitters may becellular base stations.

In one embodiment, the array response is obtained in the form of amathematical function that relates the signal response (phase andpossibly amplitude at each of the local positions) to one or moreparameters that represent the relative location between the syntheticantenna array and the transmitter. Such parameters may e.g. define adirection from the synthetic antenna array to the transmitter, aposition of the synthetic antenna array in a coordinate system at thetransmitter, or a position of the transmitter in a coordinate system ofthe portable electronic device. The step of identifying the geographiclocation may involve extracting the parameter value(s) that causes themathematical function to (approximately) result in the data samples atthe local positions. In other words, the mathematical function isoptimized for the data samples at the local positions.

In another embodiment, the array response is obtained in the form of aset of signal responses for different relative locations between thesynthetic antenna array and the transmitter, each signal response beingrepresented as phase and possibly amplitude at each of the localpositions. The step of identifying the geographic location may involvematching (correlating) the synthetic antenna array to the differentsignal responses, wherein the relative location is given by the bestmatching signal response among the set of signal responses.

The inventive method provides a number of technical advantages. Forexample, by using a synthetic antenna array, the signal receiving unitmay be provided with a simple and space-efficient antenna. Further, byusing the array response, the inventive method may be implementedwithout requiring any synchronization between the portable device andthe transmitter(s), and/or between transmitters, if the signal isrepeated and known to the portable electronic device. Furthermore, anarbitrary signal may be used since the positioning is independent ofsignal bandwidth. Thus, in contrast to the prior art, the inventivemethod also allows the use of a narrowband signal, i.e. a signal havinga bandwidth B<<c₀/a, where c₀ is the speed of light and a is therequired spatial resolution of the system. It can be noted that theinventive method works well also when the signal is an unmodulatedsinusoidal signal.

It is realized that the inventive method may be used as a replacementof, or a supplement to, conventional GNSS.

It should be emphasized that the step of identifying the geographicposition may use additional information, including but not limited tocompass information at the portable electronic device, an estimateddirection of the gravitational force at the portable electronic device,and an estimated distance between the portable electronic device and theor each transmitter. The estimated distance may be obtained with anyavailable technique, including the above-mentioned TOA and TOFtechniques.

A second aspect of the invention relates to a portable electronicdevice, comprising a signal receiving unit including an antennaconfigured to receive a signal from at least one remote transmitter; alocal positioning unit for determining a local position of the portableelectronic device; and a processor, configured to obtain a plurality ofdata samples from the signal at different time points during ameasurement period with arbitrary movement of the portable electronicdevice, associate each data sample with a local position obtained fromthe local positioning unit so as to form a synthetic antenna array,obtain an array response of the synthetic antenna array, and identifythe geographic location of the portable electronic device, by processingthe synthetic antenna array as a function of the array response and byusing knowledge about the geographic location of the or each remotetransmitter. Said antenna includes a plurality of antenna elements,wherein the processor is configured to obtain a plurality of datasamples at each local position of the apparatus.

In one embodiment, the portable electronic device may comprise a sampletimer function, configured to determine the speed or velocity ofmovement of the apparatus during the measurement period, and to controlthe sample period to target a predetermined distance between themeasurement points.

Still other objectives, features, aspects and advantages of the presentinvention will appear from the following detailed description, from theattached claims as well as from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described herein by way ofexample only, with reference to the accompanying schematic drawings.

FIG. 1 is a block diagram of a portable electronic device enablingpositioning according to an embodiment.

FIG. 2 is a flowchart of a method for operating the device in FIG. 1.

FIG. 3 is a block diagram of a positioning system on a mobile phoneaccording to an embodiment.

FIG. 4 is flowchart of a method for operating the device in FIG. 3.

FIG. 5 is a definition of coordinates and vector for positioning of aportable electronic device once angle-of-arrival estimates are known.

FIG. 6A-6C are diagrams to exemplify the required information forpositioning when different number of sources are available.

FIG. 7 is a definition of angles-of-arrival in elevation and azimuth.

FIG. 8 is an illustration of a correlation between positioning by meansof a synthetic array and a time of arrival calculation.

FIG. 9 shows an example of positioning by means of direction estimationfrom wireless access points, improved by correlation with a cellularbase station time difference measurement.

FIG. 10 shows an example of positioning by means of direction estimationand distance estimation, based on signalling with only one networktransmitter.

FIG. 11 schematically illustrates movement of an apparatus, so as tocreate a synthetic antenna array from a physical antenna array.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a schematic illustration of an implementation of a portableapparatus 100, typically in the form of a handheld electronic device,which is operable to receive a signal from a source 200. The signal istransmitted as electromagnetic waves that propagate from the source 200to the apparatus 100, typically as radio waves or microwaves. Normally,the geographic location of the source 200 is not known to the apparatus100. Generally, the source 200 is stationary, i.e. has a fixedgeographic location.

The apparatus 100 includes a processor 102, a storage device 104, areceiver or transceiver 106, an antenna 108 and a motion detector 110.In combination, the components 102-110 may cooperate to obtain data thatenables determination of the direction between the source 200 of thesignal and the apparatus 100, and given the geographic location of thesource 200 and possibly additional input as well as, it is possible todetermine the geographic location of the apparatus 100 (in the globalcoordinate system XYZ). As will be explained in detail further below,the additional input may comprise information about a cardinal directionof a compass, the direction of the gravitational force, an estimateddistance from the apparatus 100 to the source 200, or one or moreadditional estimated directions to one or more additional sources (notshown in FIG. 1). Each such additional estimated direction to anadditional source may be determined in the same way as the direction tothe source 200. Alternatively, the additional input may be obtained froma time difference measurement, of signals from one or more transmittersreceived in the apparatus 100.

In order to estimate the direction between the apparatus 100 and thesource 200, the apparatus 100 is configured to obtain a data set byreceiving and sampling the signal at different time points while theapparatus 100 and thus the antenna 108 is moved along a randomthree-dimensional trajectory 140, as indicated in FIG. 1. The samplingthus results in a set of spatial measurement points m₁-m₁₈, alsoindicated in FIG. 1. Each measurement point m₁-m₁₈ represents one ormore properties of the signal, including at least the phase of thesignal, and possibly the amplitude of the signal, as sampled at therespective time point. It is to be noted that the resulting set ofmeasurement points m₁-m₁₈ does not need to be located in a spatiallyuniform pattern, but could be completely random. Concurrent with thesampling of the signal, positional data is obtained from the motiondetector 110. Depending on the required accuracy, the positional datamay indicate the relative or absolute location of the apparatus 100 in alocal coordinate system, or the corresponding location of the antenna108 (i.e. accounting not only for translation but also rotation of theapparatus 100), for each measurement point m₁-m₁₈. The local coordinatesystem is defined in relation to the apparatus 100 and has no predefinedrelation to the global coordinate system XYZ.

A measurement signal may thereafter be generated, and transmitted fromthe apparatus 100 to the network, typically to the currently servingbase station or access point. For each transmitted radio signal, themeasurement signal may comprise a plurality of data samples, such asm₁-m₁₈, obtained in the apparatus from the respective transmitted signalat different time points during a measurement period with movement. Themeasurement signal may also comprise local position data associated toeach data sample obtained from a local positioning unit in theelectronic device, so as to form a synthetic antenna array. Furtherprocessing of the sampled signal is then preferably performed in thenetwork, such as in a node connected to the serving base station.

In the following, for explaining the processing of the sampled signal,reference is made to the theoretical framework presented by A. Richterin “Estimation of radio channel parameters: Models and algorithms”,Ph.D. Dissertation, Technische Universität Ilmenau, Ilmenau, Germany(2005), which is incorporated herein in its entirety by reference.

By associating each measurement point m₁-m₁₈ with a local position, itis possible to treat the resulting data set as a synthetic/virtualantenna array, see e.g. A. Richter (2005), Chapter 3.3, and thus toprocess the data set by any one of a multitude of known directionalestimation algorithms based on antenna array measurements, see e.g. H.Krim and M. Viberg: Two decades of Array Signal Processing Research,IEEE Signal Processing Magazine, pp 67-94, July 1996. Such directionalestimation algorithms, commonly denoted DOA (direction of arrival)algorithms, enable directional estimation based on a data set of signalproperties sampled at a sufficient number of spatially separatedpositions with sufficiently well-defined coordinates. Those samples canbe measured either by a synthetic/virtual array or a physical array.Common to such DOA algorithms is that they define a function thatrelates the phase of the signal, and possibly the amplitude of thesignal, at different positions to the direction of arrival of the signalat the antenna array. It should be noted that in the case of asynthetic/virtual array, a single antenna used does not need to becharacterized in gain and phase response. This in contrast to physicalarrays, where it may be important to know the variations between theindividual antenna elements used. It is advantageous if the referencedirection of a single antenna stays the same during the measurementinterval, though this is not a strict requirement.

To further explain and exemplify the use of DOA algorithms, consider anantenna with a single antenna element 108 that is receiving a signalfrom a single source 200 in free space. The complex base bandrepresentation of the signal from the source transmitted at time instantt_(i) is denoted s(t_(i)). This complex base band signal may be anarbitrary signal, modulated or non-modulated (s(t_(i))=1). Assume thatthe transmit filter has an impulse response g_(T)(t) and the receivefilter has an impulse response g_(R)(t). The complex basebandrepresentation of the received signal is then given by (see e.g. Richter(2005), Chapter 2.2):

r(t _(i))=s(t_(i) −l _(p) /c ₀)*g _(R)(t)*g _(T)(t)A exp{−j2πf _(c) l_(p) /c ₀},

where ‘*’ denotes convolution, c₀ is the speed of light, l_(p) is theelectrical length of the propagation path, f_(c) is the carrierfrequency and A includes free space path loss and complex antenna gain.An equivalent frequency domain representation is given by:

R(f)=S(f)G _(R)(f)G _(T)(f)A exp{−j2πfτ _(p)}exp{−j2πf _(c) l _(p) /c₀},

where τ_(p)=l_(p)/c₀ is the time delay from the source to the receiver.

For time of arrival based methods, such as TOA and TOF, the time delayor relative time delay can be extracted from a single measurement ofr(t_(i)) by considering the impulse response (or any equivalent measure)of the channel that can be extracted by help of a transmitted broad bandsignal S(f). One embodiment of the inventive method for positioning isnot based on such time delays, but on the array response of thesynthetic antenna array created when the antenna 108 is moved in avolume and the received signals are sampled at different positions(measurement points m₁-m₁₈). The “array response”, which is a well-knownterm to the person skilled in the art, refers to the M×1 complex arrayresponse of the synthetic antenna array built up from the differentmeasurement positions to a (unit-power) source in the direction (θ, φ),where θ, are the elevation and azimuth angles-of-arrival, respectively,from the source and M is the number of measurement points. Furtherdetails may be found in “Antenna Array Mapping for DOA Estimation inRadio Signal Reconnaissance” by P. Hyberg, Ph.D. Dissertation, RoyalInstitute of Technology, Stockholm, Sweden (2005), which is incorporatedherein in its entirety by reference.

For small movements, e.g. occurring when the portable apparatus 100 ismoved by its user, it is possible to neglect the changes in the delayτ_(p) between the measurement points, unless the observation bandwidthis really large. This is true if the movement is significantly smallerthan c₀/B, where c₀ is the speed of light and B is the observationbandwidth, see Richter (2005), Chapter 2.2. It is further possible todecompose the array response, see Richter (2005), Chapter 2.4.2, into anelement beam pattern shared by the antenna element 108 in all itspositions (measurement points) and a phase vector relating the positions(measurement points) within the synthetic antenna array to the phases ofthe array response.

As will be exemplified further, the array response (e.g. given by itsphase vector) is used for determining the direction to the source 200from the synthetic antenna array. Assume that the signal is measured ata local coordinate x_(i)∈R^(3×1). The frequency representation of thereceived signal may then be described by

R(f)=S(f)G _(R)(f)G _(T)(f)A ₀ exp{−j2πfτ _(p)}exp{−jk _(0n) x _(i) ^(T)k _(n)},

where k_(n)=−[cos φ_(n) sin θ_(n) sin φ_(n) sin θ_(n) cos θ_(n)]^(T),θ_(n) and φ_(n) are the elevation and azimuth angles-of-arrival,respectively, from the source 200, k_(0n)=2πλ_(n) ⁻¹, λ_(n) is the(carrier) wavelength of the signal from the source 200, and λ₀represents the free space path loss and complex antenna gain includingthe reference phase at the origin of the local coordinate system. Theposition specific part of the array response is given byexp{−jk_(0n)x^(T)k_(n)}, where x is a matrix representation of thelocations of all measurement points in the local coordinate system. Byestimating the local positions of the measurement points by help of themotion detector 110, it is possible to form the position specific partof the array response. With this antenna array response, considering themeasured phase changes during the movement, it is possible to determinethe direction to the source 200.

Given that there are enough sources available and that the locations ofthose sources are known, it is possible to determine the location(global position) of the receiving antenna. Note that the phase isindicative of the directions to the sources and that this technique doesnot depend on the time for the signal to travel from the source to thereceiver. The technique thereby works for arbitrary signals s(t_(i))from the source. For multipath channels, which are predominant forwireless communication, it should be noted that there is one phase andamplitude term associated with each multipath component and it is theincoming angle of the multipath component that is estimated.

Since the resulting data set may be treated/processed as asynthetic/virtual antenna array, the apparatus 100 may be provided witha simple and space-efficient antenna 108, which does not enabledirectional estimation in itself, since the resulting data set istreated/processed as a synthetic/virtual antenna array as describedabove. Further, the embodiment in FIG. 1 enables determination of thegeographic location of the apparatus 100 without requiring access to aGNSS, such as a built-in GPS receiver.

FIG. 11 shows an embodiment, in which a multi-element antenna is moved,so as to form the synthetic antenna array. In the embodiment describedwith reference to FIG. 1, the time sample separation in the syntheticarray may correspond to the wavelength separation, dependent on thedevice movement v and carrier frequency fc. As an example for LTE, withfc=700 MHz, samples captured every 10 ms, and v=1 m/s, the distancebetween each sample point would be about λ/4, where λ is the signalwavelength. However, due to restricted accuracy of the motion detector110, an error in the local position determination between a first andsecond sample, will be added to another error in the local positiondetermination between the second and a third sample, and so on. In oneembodiment, as exemplified by the drawing of FIG. 11, this drawback isovercome by using a physical antenna array to form a synthetic antennaarray. In this embodiment, antenna 108 comprises two or more antennaelements, such as 2, 3, 4, 5 or more. To use a multi-element physicalantenna to sense direction has as such been described before. However,the inventors have realized that the inventive combination of a physicalmulti-element antenna with a synthetic/virtual array generated bymovement, provides an improvement. For one thing, the movement to obtaina plurality of samples, as indicated in FIG. 1, provides a longer andmore extensive spatial trajectory than any physical array confined in anapparatus 100 of compact size, such as a mobile phone, a computer, asurf pad, or similar. On the other hand, the positional relation betweenthe elements of a physical antenna is much more precisely defined, bymeans of the mechanical structure, than the positions detected by amotion detector 110. This brings about an aggregate technical effect.Furthermore, multi-element antennas are more robust for a large range offrequencies fc=700 MHz to 30 GHz.

In the embodiment of FIG. 11, the apparatus 100 comprises amulti-element physical antenna 108 including three antenna elements1081, 1082, 1083. In this drawing, the antenna 108 is indicated by meansof a dash-dotted encircling of the antenna elements 1081, 1082, 1083. Inorder to estimate the direction between the apparatus 100 and a source(not shown), the apparatus 100 is configured to obtain a data set byreceiving and sampling a signal from the source at different time pointswhile the apparatus 100 and thus the antenna 108 is moved along a randomthree-dimensional trajectory 140, as indicated in FIG. 11. In thedrawing, this is illustrated by respective trajectories for the antennaelements 1081, 1082, 1083, in the form of dashed lines. The samplingthus results in a set of spatial measurement points, similar to theembodiment of FIG. 1. However, for this embodiment, three samplesm_(1,x), m_(2,x), m_(3,x) are obtained in each position of the apparatus100. Had the apparatus comprised e.g. four antenna elements, foursamples would have been obtained in each measurement point. Eachmeasurement point represents one or more properties of the signal,including at least the phase of the signal, and possibly the amplitudeof the signal, as sampled at the respective time point, for therespective antenna element 1081, 1082, 1083. The sampling through thedifferent antenna elements 1081, 1082, 1083 may be executedsimultaneously, or e.g. cyclically. Otherwise, further featuresdescribed with reference to FIG. 1 apply also to the embodiment of FIG.11. For the sake of simplicity, these features and elements (102, 104,106, 110) shown for apparatus 100 in FIG. 1, are not set out in FIG. 11,nor is the description thereof repeated with reference to FIG. 11.However, it will be understood that sampling can be made at fewer localpositions with the embodiment of FIG. 11, while still collecting as manysamples, compared to a single antenna solution, such as the one inFIG. 1. Also, determination of the local position (and spatialrotational orientation) of the apparatus 100 when taking the samples,will be improved with respect to a single antenna solution, since therelative distance and orientation of three sample points will always begiven, within the accuracy of the mechanical structure of the apparatus.Or, conversely, with the same sample frequency, collecting three samplesper cycle rather than one, means that more samples are collected for agiven time period. This may result in a richer data set to subsequentlycalculate the direction from.

A measurement signal may thereafter be generated, and transmitted fromthe apparatus 100 to the network, typically to the currently servingbase station or access point. For each transmitted radio signal, themeasurement signal may comprise a plurality of data samples, such as(m_(1,1), m_(2,1), m_(3,1)) to (m_(1,3), m_(2,3), m_(3,3)), obtained inthe apparatus from the respective transmitted signal at different timepoints during a measurement period with movement. It may be noted thatmore than three sample periods may be carried out, whereby each sampleperiod will render another set of three samples. The measurement signalmay also comprise local position data associated to each data sampleobtained from a local positioning unit in the electronic device, so asto form a synthetic antenna array. Further processing of the sampledsignal is then preferably performed in the network, such as in a nodeconnected to the serving base station.

It is also conceivable to combine the embodiments in FIGS. 1 and 11,respectively, with a GNSS. For example, the apparatus 100 may include aGPS receiver (not shown), whereby the apparatus 100 may be operated inaccordance with the inventive concept to provide navigational datawhenever the GPS receiver fails to receive the required satellitesignals or fails to determine a geographic location based on thesesatellite signals.

It is also conceivable to use the navigational data provided by theinventive positioning system to supplement the output data ofconventional positioning systems, e.g. to reduce the impact of errorpropagation in such output data. Such conventional positioning systemsexhibiting problems with error propagation include step counters andpedometers.

The data set may be collected after first instructing the user of theapparatus 100 to manually impart the random movement to the apparatus100. The user may be instructed via any form of user interface (notshown) on the apparatus 100, e.g. a loudspeaker or a display screen. Forexample, the user may be instructed to wave the apparatus 100 in theair. Alternatively, the data set may be collected based on “natural”user movements, e.g. while the apparatus 100 is carried around by theuser or while the apparatus 100 is located in a moving vehicle.

In one embodiment, the apparatus 100 is configured to take into accountthat the speed of the movement is not predetermined In this embodiment,a sample timer function is functionally included in the apparatus 100,e.g. in the processor 102. Samples taken with a distance of λ betweeneach other or not useful for the synthetic antenna array. Therefore, thesample timer function is configured to determine the speed, or velocity,of movement of the apparatus during the measurement period. This may bedetermined by means of a motion detector 110. The sample timer functionis further configured to control the sample period to target apredetermined distance between the measurement points, e.g. in theregion of λ/4 of the frequency of the signal measured. This embodimentmay apply both to a single antenna solution, and to an apparatus withplural physical antenna elements.

The apparatus 100 (its receiver/transceiver 106) should be coherent withthe source 200 during the measurement period such that only minimalfrequency drift is allowed between the source 200 and thereceiver/transceiver 106. In other words, all phase and amplitudevariations of the received signal over the different measurement pointsshould be predominantly or exclusively caused by the movement of theapparatus 100. The signal may be a repeated signal, i.e. a known orunknown signal transmitted at some specific time instants, and/or asignal known to the apparatus 100 but not necessarily repeated. Theimportant aspect is that the apparatus 100 is able to distinguish thephase and amplitude variations caused by the movements from those causedby the transmitted signal. Furthermore, the signal may be broadband ornarrowband since transmit times are not used for the directionalestimate. If the signal is repeated and has a given coherence time, theapparatus 100 may be configured to actively set the measurement periodnot to exceed this coherence time. The coherence time of anelectromagnetic signal is the time over which a propagating wave may beconsidered coherent, i.e. it is the time interval within which its phaseis predictable. It is conceivable that the apparatus 100 (thereceiver/transceiver 106) is actively synchronized with the remotesource 200 before and/or during the measurement period.

It is currently believed that an adequate accuracy of the estimateddirection of the source 200 (or alternatively, the geographic locationof the apparatus 100) is obtained for a data set containing at least 3measurement points, and preferably at least 8 measurement points, atleast 20 measurement points or at least 30 measurement points. Apartfrom the computational complexity, and the bandwidth required forsending the data to the network for processing, there is no upper limitfor the number of measurement points acquired during a measurementperiod. It is well known that the variance of the directional estimatedecreases when the antenna array aperture is increased, see e.g. Richter(2005), Chapter 3.3. Usually the aperture is between one and up to acouple of wavelengths, but it may be smaller as well as considerablylarger.

Generally, each measurement period is dedicated to sampling of thesignal originating from a specific source 200. Thus, if the apparatus100 is to receive signals from plural sources, the apparatus initiatesone measurement period for each source. However, from the user'sperspective this sequence of measurement periods could be merged intoone session for navigational positioning of the apparatus. If thehardware of the apparatus 100 allows it, the measurements of severalsources may be performed in a parallel fashion as well.

Returning to the example in FIG. 1, the processor 102 is connected toreceive an input from the motion detector 110. The motion detector 110may be, for example, an inertial measurement unit (IMU), which mayinclude a three dimensional accelerometer configured to detecttranslation of the apparatus 100 in any direction. The IMU may, forexample, also comprise a magnetometer and/or a gyrometer for detectingrotation of the apparatus. Alternatively, the motion detector 110 may bebased on any other available technology for relative or absolutepositioning, including but not limited to odometers, laser basedrangefinders (provided by e.g. Hokuyo Automatic Co, Ltd), ultrasonicrangefinders (e.g. by Maxbotics Inc), camera based positioning, eitherbased on single (e.g. by Mesa Imaging AG) or multiple cameras (e.g. byNASA) or by a camera replacing the IMU, operating with Simultaneouslocalization and mapping (SLAM). As noted above, these elements may alsoform part of the apparatus of the embodiment shown in FIG. 11.

The processor 102 may be any type of processing circuitry. For example,the processor 102 may be a programmable processor that interpretscomputer program instructions and processes data. Alternatively, theprocessor 102 may be, for example, programmable hardware with embeddedfirmware. The processor 102 may be a single integrated circuit or a setof integrated circuits (i.e. a chipset). The chipset may be incorporatedwithin a module, which may be integrated within the apparatus 100,and/or may be separable from the apparatus 100. The processor 102 mayalso be a hardwired, application-specific integrated circuit (ASIC).

The processor 102 is connected to receive an input from thereceiver/transceiver 106. The receiver/transceiver 106 may be operableto receive the above-mentioned signal(s), and to transmit other signals,such as the measurement signal. The receiver/transceiver 106 isconnected to the antenna 108. In one embodiment, the antenna 108 has asingle antenna element for receiving the signal(s). In anotherembodiment, such as the one shown in FIG. 11, the antenna 108 maycomprise a number of antenna elements 1081, 1082, 1083. The processor102 is also connected to read from and write to the storage device 104.The storage device 104 is, in this example, operable to store computerprogram instructions, and may be a single memory unit or a plurality ofmemory units. If the storage device 104 comprises a plurality of memoryunits, part or the whole of the computer program instructions may bestored in the same or different memory units.

The computer program instructions stored in the storage device 104control the operation of the apparatus 100 when loaded into theprocessor 102. The computer program instructions provide the logic androutines that enable the apparatus 100 to perform the steps performedtherein of the methods illustrated in FIGS. 2 and 4, and describedbelow. The computer program instructions may arrive at the apparatus 100via an electromagnetic carrier signal or be copied from a physicalentity such as a computer program product, a memory device or a recordmedium such as a CD-ROM or DVD.

FIG. 2 is a flow chart of an exemplifying method for positioning of theapparatus of FIG. 1 or 11. In this embodiment, at step 205, radiosignals are transmitted from one or more network transmitters, whichsignals are received in the apparatus 100. At step 210 in FIG. 2, theapparatus 100 is operated to obtain a plurality of data samples from thesignal at different time points during the measurement period witharbitrary movement of the apparatus 100. Depending on implementation,the data samples may be extracted from the signal by either thereceiver/transceiver 106 or the processor 102, or a combination thereof.As indicated above, each data sample represents the phase of the signal,and may also represent the amplitude of the signal. At step 220, theapparatus associates each data sample with a local position obtainedfrom the motion detector 110 for forming a synthetic antenna array. Inone embodiment, the formation of the synthetic antenna array isperformed by the processor 102, which obtains the positional data foreach data sample from the motion detector 110. In another embodiment,the formation of the synthetic antenna array is performed later, in thenetwork. At step 225, a measurement signal is transmitted from theapparatus 100 to the network, preferably via the access point or basestation currently serving the apparatus 100. At step 230, the arrayresponse of the synthetic antenna array is obtained. At step 240, thesynthetic antenna array is processed as a function of the array responseobtained in step 230, to identify the relative location of the apparatus100 and the source 200 (e.g. given by the direction to the source 200),and identifies the geographic location of the apparatus 100 using therelative location and the known geographic location of the source 200.Below follows a detailed example of one embodiment. Reference will bemade to reception of GSM signals, i.e. the apparatus 100 is a mobilecommunications terminal adapted for communication over a GSM system.However, reference is also made to LTE, in particular for certainspecific embodiments. I is to be understood that the illustratedembodiment is not limited to neither GSM nor LTE systems, though, butthe mobile communications terminal could operate on signals from anytype of available source with a known geographic location, includingwireless access points (WAP) for local area networks (e.g. the IEEE208.11 family), base stations (BS) for any type of cellular system(e.g., GSM, W-CDMA, WiMAX, IS-95, CDMA2000, D-AMPS, EV-DO), as well asdedicated transmitters.

FIG. 3 is a block diagram of a positioning system 500 for obtaining thelocation of a mobile communications terminal 100. The positioning system500 is employed in one or more entities connected to a network oftransmitters 200, 300, 400, and operates in cooperation with a terminal100 to be positioned. For the purpose of wireless communication, thepositioning system 500 is connected to a network transmitter andreceiver 200, which in turn includes an antenna. For the example of anembodiment in LTE, the positioning system 500 may include or form partof a location server LS, and the network transmitter 200 may be aneNodeB 200. In such an LTE embodiment, the positioning system 500 may beconnected to the eNodeB 200 via an MME (Mobility Management Entity), andmay include an E-SMLC (Evolved Serving Mobile Location Center). In anyinstance, the positioning system 500 may comprise a transceiver unit 502for communication with the network transmitters 200, 300 300, and acontroller 550. In the controller 550, there is a processor 510, e.g. aCPU, and a storage device 504 comprising computer code, and a databaseof base stations and their geographic locations (e.g. GPS coordinates),and possibly also the frequencies they are using. In an alternativeembodiment, such geographic location data for the network transmittersis stored remotely in the network, and is retrieved by datacommunication when needed.

FIG. 4 is a flowchart to exemplify the operation of the positioningsystem 500 in FIG. 3, in cooperation with the apparatus 100 to bepositioned. The apparatus 100 may initially scan the frequency spectrumfor available base stations in step 402. This process normally formspart of standard behaviour in cellular networks, for the purpose ofhandover preparation. However, dependent on the embodiment, thepositioning of the apparatus 100 need not be based on the pilot signalsotherwise used for signal strength measurements. As an exemplaryalternative, the directional estimation may be carried out by makingmeasurements on Position Reference Signals (PRS). In a GSM embodiment,the apparatus may measure a repeated signal, such as the synchronizationsequence inside the GSM synchronization burst or the training sequencein a normal GSM burst. The process flow may continue with a step ofensuring that the apparatus 100 to position is subjected to an arbitrarymovement during the directional estimation. This may be effected byoutputting instructions to the user via a user interface. Alternatively,step 404 may be replaced or supplemented by a step of monitoring theoutput signal of the motion detector 110 to verify that the apparatus100 is in adequate motion. However, rather than carrying out that stepbefore synchronization with a base station, it may be carried out aftersynchronization, which is the embodiment shown in the example of FIG. 4.

For each identified base station 200-400, the apparatus 100 executes asequence of steps 404-410 that collectively define a measurement period.In step 404, the system locks the RF processing unit 106 of theapparatus 100 to the base station frequency of a first base station 200to get coherent reception, unless this step has already been carriedout, e.g. if base station 200 is the currently serving base station. Forthe example of GSM this may be done by listening to the frequencycorrection channel (FCCH) in and correcting any frequency offset betweenthe local oscillator in the RF processing unit 106 and in the basestation 200. The RF processing unit 106 may also find timesynchronization by listening to the synchronization channel (SCH). Oncetime synchronization is established, the base station ID may beobtained, e.g. from the broadcast control channel (BCCH) in a GSMsystem.

In step 406, it is ensured that the apparatus 100 to position issubjected to an arbitrary movement during the directional estimation, asalready outlined above.

Accordingly, the apparatus 100 is connected to and knows the ID of thebase station, the RF processing unit 106 starts measuring the phase andamplitude variations of a repeated, usually known, signal when theantenna 108 is moved while the output signal from the local positioningunit 110 simultaneously is recorded so that the physical movement of theantenna 108 may be calculated between the measurement points and hencethe local coordinates of the measurement points may be calculated (step408). In this way the received phase and amplitude of the receivedsignal is recorded in several random, but known, positions. Assumingthat the environment is static and the only movement is that of thereceiving antenna 108, the digital signal processing unit 102 may form asynthetic/virtual antenna array. Preferably though, the apparatus isconfigured to transmit a measurement signal to the network, typicallyvia the serving base station, for further processing. This way,processing required for obtaining an estimate of the position of theapparatus is saved in the apparatus. As a consequence, the inventivemethod provides a method for positioning that requires less power in theapparatus 100 than other technologies.

The apparatus 100 then repeats steps 404-410 for each further basestation 300, 400 identified in step 402 (step 412). Optionally, theapparatus 100 may limit the processing to a given number of basestations, e.g. a number deemed to result in a sufficient accuracy of thegeographic location to be calculated in step 418. In one embodiment,measurements are only carried out for one base station 200, as isoutlined with respect to the embodiment of FIG. 10.

For the or each base station, for which a measurement signal has beentransmitted from the apparatus 100, an estimate of a direction betweenthat base station and the apparatus 100 is then established. This maye.g. entail known DOA algorithms, e.g. beamforming techniques such asBartlett beamforming or Capon beamforming, or known parameter estimationmethods such as SAGE to estimate the direction α_(i) of the incomingsignal (step 414). These techniques may presume that the received signalis a sum of plane waves, but there are also available techniquesdesigned to handle near-field effects. This direction is often similarto the physical direction to the base station 200, but may vary due toobstructions of the signal path.

By carrying out the direction estimation in the network, it is possibleto correlate or otherwise combine the geographic location informationobtained from processing the synthetic antenna array with timedifference measurements. In a preferred embodiment, OTDOA measurementscarried out by the apparatus are also transmitted as a measurementsignal to the network. In one embodiment, the samples measured for thesynthetic antenna array and OTDOA measurements made on a PRS of the samebase station may be collectively transmitted in one measurement signal.Alternatively, e.g. if these measurements are carried out on differentsignals, and/or with different timing requirements, these measurementsignals 410 may be transmitted independently. When all iterations ofsteps 406-412 are completed, the system 100 has access to a set ofdirectional estimates (α_(i)) to the different base stations 200-400. Instep 416, the geographic position of those base stations are obtainedfrom memory storage 504.

Optionally, the digital signal processing unit 102 may also obtaincompass information and/or the direction of the gravitational force,i.e. an indication about the orientation of the apparatus 100 inrelation to the coordinate system of the geographic locations, and sendit with the measurement signal (step 410). The compass information may,e.g., identify the direction of one of the cardinal directions of thecompass. Such compass information may be obtained from a magnetometer oranother type of magnetic sensor in the apparatus 100. The direction ofthe gravitational force may, e.g., be obtained by accelerometers.

Based on the available data (direction(s), and possibly distance(s)and/or compass information), the processor 510 estimates the geographiclocation of the apparatus 100 by means of triangulation (step 418). Theestimated location may be derived as a position on a map where theavailable data has the best match to all available base stations200-400. The estimated geographic location may be transmitted to theapparatus 100 for display to the user, or e.g. to a rescue service.

It should be realized that the inventive positioning system may beadvantageously implemented on existing portable electronic devices, andin particular on radio communication devices such as mobile phones. Whenimplemented on mobile phones, the positioning system may use theexisting mobile communication infrastructure such as base stations, andinvolve only minor modifications of the mobile phones, typically byinstalling dedicated software. It should be noted that the directionalestimation and positioning may be performed without support from thecellular network as long as the geographic locations of the surroundingbase stations are known to the mobile phone. It should also be notedthat many modern mobile phones have built-inaccelerometer/gyrometer/magnetometer and/or cameras which may be used inthe inventive positioning system.

By implementing the inventive positioning system in mobile phones, it ispossible to fulfil existing and future legal requirements (e.g. in theU.S.) that mobile phones should enable automatic positioning, whenmaking emergency calls, without access to a GNSS.

The triangulation step 418 (FIG. 4) will now be further exemplified withreference to FIG. 5, which illustrates the system 100′ in a globalCartesian coordinate system, after determination thedirections-of-arrival to N sources (base stations). The task is now todetermine the geographic location of the system 100′ given by p=[p_(x)p_(y) p_(z)]^(T) where [•]^(T) denotes the transpose operation. Thedirections of arrival from source n in the azimuth and elevation planes,φ_(n) and θ_(n), respectively, are related to the direction vector k_(n)by

k _(n)=[cos φ_(n) sin θ_(n) sin φ_(n) sin θ_(n) cos θ_(n)]^(T)

which may be related to p and the position of source n, whosecoordinates b_(n)=[b_(nx) b_(ny) b_(nz)]^(T) are known to the system100′, by

$k_{n} = \frac{b_{n} - p}{d_{n}}$

where d_(n) is the distance between p and source n given by

d _(n)=√{square root over ((b _(n) −p)^(T)(b _(n) −p))}.

If the system 100′ does not know its rotation relative the globalcoordinate system, it does not know k_(n) explicitly, but only the angleα_(mn) between each two direction vectors k_(m) and k_(n), which isgiven by their scalar product as

cos α_(mn)=k_(mn) ^(T)k_(n)

Note that α_(mn) is independent of the coordinate system.

If signals from three sources 200, 300 and 400 are available, asillustrated in FIG. 6A, the system 100′ may estimate its positionwithout knowing its rotation relative the global coordinate system,i.e., without explicit knowledge of the direction vectors k₂₀₀, k₃₀₀ andk₄₀₀. This is done by solving the equation system:

$\quad\left\{ \begin{matrix}{\frac{\left( {b_{200} - p} \right)^{T}\left( {b_{300} - p} \right)}{\sqrt{\left( {b_{200} - p} \right)^{T}\left( {b_{200} - p} \right)\left( {b_{300} - p} \right)^{T}\left( {b_{300} - p} \right)}} = {\cos \; \alpha_{200,300}}} \\{\frac{\left( {b_{200} - p} \right)^{T}\left( {b_{400} - p} \right)}{\sqrt{\left( {b_{200} - p} \right)^{T}\left( {b_{200} - p} \right)\left( {b_{400} - p} \right)^{T}\left( {b_{400} - p} \right)}} = {\cos \; \alpha_{200,400}}} \\{\frac{\left( {b_{300} - p} \right)^{T}\left( {b_{400} - p} \right)}{\sqrt{\left( {b_{300} - p} \right)^{T}\left( {b_{300} - p} \right)\left( {b_{400} - p} \right)^{T}\left( {b_{400} - p} \right)}} = {\cos \; \alpha_{300,400}}}\end{matrix} \right.$

If signals from two sources 200 and 300 are available and the system100′ has access to compass information and the direction of thegravitational force, i.e., knows the direction vectors k₂₀₀ and k₃₀₀, asillustrated in FIG. 6B, the system 100′ may estimate its position bysolving the equation system:

$\quad\left\{ \begin{matrix}{{p - b_{200} + {d_{200}k_{200}}} = 0} \\{{p - b_{300} + {d_{300}k_{300}}} = 0}\end{matrix} \right.$

Note that the system 100′ does not have to know the distances d₂₀₀ andd₃₀₀.

If the signal from a single source 200 is available, and the system 100′has access to compass information, the direction of the gravitationalforce, and knows the distance to the source, as illustrated in FIG. 6C,it can estimate its position by solving the equation:

p−b ₂₀₀ +d ₂₀₀ k ₂₀₀=0.

It is to be understood that the above examples indicate the requiredminimum number of sources. In a practical situation, it may be desirableto use an increased number of sources, e.g. to improve accuracy orrobustness via redundancy in the positional estimation.

Looking now in more detail at techniques for estimating the geographiclocation based on estimated directions only, these techniques may bedivided into two major categories: explicit triangulation and inherenttriangulation.

In explicit triangulation, a cost function f(θ_(n), φ_(n)) may bedefined for each source (base station) n to include the directionalestimation (DOA) algorithm (e.g. a synthetic antenna array algorithm),given as a function of the elevation angle (θ_(n)) and the azimuth angle(φ_(n)), for the synthetic antenna array defined by the sampled data(e.g. phase and local position). The definition of the angles θ, φ forthe direction vector k is given in FIG. 7. The cost function isminimized for the angles {{circumflex over (θ)}_(n), {circumflex over(φ)}_(n)}. Thus, for each source, the following optimization isexecuted:

$\left\{ {{\hat{\theta}}_{n},{\hat{\phi}}_{n}} \right\} = {\underset{\theta_{n},\phi_{n}}{\arg \; \min}\; {f\left( {\theta_{n},\phi_{n}} \right)}}$

The estimated direction to the source is given by {circumflex over(θ)}_(i). The geographic location of the apparatus is then estimated byminimizing another cost function J({circumflex over (θ)}₁, {circumflexover (θ)}₂, . . . , {circumflex over (θ)}_(N)), N being the number ofavailable sources. The cost function J may be based on an explicittriangulation of the estimated direction, such that minimizing the costfunction J finds the most likely intersection point for all estimateddirections.

In inherent triangulation, a cost function g(θ₁, φ₁, θ₂, φ₂, . . . ,θ_(N), φ_(N)) may be defined for all N sources to include thedirectional estimation (DOA) algorithm (e.g. a synthetic antenna arrayalgorithm), given as a function of the elevation angles (θ₁, . . . ,θ_(N)) and the azimuth angles (φ₁, . . . , φ_(N)), for the ensemble ofsynthetic antenna arrays defined by all data samples. Thus, theoptimization of this cost function directly yields the estimatedgeographic location, i.e. without first estimating the individualdirections to the sources:

$p = {\left\lbrack {p_{x}\mspace{20mu} p_{y}\mspace{20mu} p_{z}} \right\rbrack^{T} = {\underset{\theta_{1},\phi_{1},\theta_{2},\phi_{2},\ldots \;,\theta_{N},\phi_{N}}{\arg \; \min}{g\left( {\theta_{1},\phi_{1},\theta_{2},\phi_{2},\ldots \;,\theta_{N},\phi_{N}} \right)}}}$

It should be understood that the cost function g does not need to bedefined as a function of elevation and azimuth angles, but could insteadbe defined based on a so-called state space model for the relevantunderlying process which, as explained above, is based on the arrayresponse of the synthetic antenna array. Thus, the cost function g maybe defined to directly relate the estimated geographic location to thearray response. It should also be realized that the minimization of acost function is merely given as an example, and both the explicittriangulation and the inherent triangulation could involve optimizationof other types of functions.

Explicit triangulation generally involves a lower mathematical andcomputational complexity, and it does not have to be designed for apredetermined number of available sources. If the minimization of thecost function f results in a majority of correctly estimated directionsto the different sources, the explicit triangulation will be able toidentify the geographic location of the apparatus as the intersectiongiven by the majority of estimated directions. Typically, incorrectlyestimated directions result from signal reflections, and thus originatefrom incoming signals of reduced signal strength. If the signalsreceived from all sources have essentially equal (high) signal strength,the explicit triangulation might be suboptimal and it may beadvantageous to use the inherent triangulation instead. The inherenttriangulation does not estimate the directions to the sourcessequentially, but instead the directions are embedded as parameters inan overall function (signal model) and the estimated geographic locationis obtained by optimizing all angles collectively.

In one embodiment, the positioning process may actively switch betweenthe inherent and explicit triangulation based on the signal strengths ofthe individual incoming signals and/or the number of available sources.As indicated above, there are numerous available synthetic/virtualantenna array algorithms that may be applied directly, or aftermodification, for directional estimation. Such algorithms include bothbeamforming algorithms and parameter estimation algorithms. Yet anothersimplified DOA algorithm for directional estimation is given below.

Consider an antenna with a single antenna element, and a receiver thatis continuously receiving signals from N sources (base stations). Thereceiver (antenna) is moved in a volume and the received signals aresampled at the time instances t₀, . . . , t_(k−1). The local coordinatesof the receiver (antenna) are determined at the time instances t₀, . . ., t_(k−1) using the motion detector. The sampled signal data, which maybe measured in a sequential or parallel manner, is stored in a matrixs∈C^(N×k), where each row s_(n) contains k signal samples from source n.The local coordinates are stored in a matrix x∈R^(3×k). The (complexbase band) signal from source n received at time instant t₁ is denoteds_(ni), whereas the coordinate vector for this signal sample isx_(i)∈R^(3×1). The signal samples are used to form a synthetic antennaarray, which for each source n has an array response

a _(n)(θ,φ)=exp{−jk _(0n) x ^(T) k}

where θ and φ are the elevation and azimuth angles-of-arrival,respectively, k=−[cos φ sin θ sin φ sin θ cos θ]^(T), k_(0n)=2πλ_(n) ⁻¹and λ_(n) is the (carrier) wavelength of the signal from source n. Foreach source n, the elevation and azimuth angles-of-arrival are derivedfrom

$\left\{ {{\hat{\theta}}_{n},{\hat{\phi}}_{n}} \right\} = {\underset{\theta,\phi}{\arg \; \min}\left\{ \frac{{a_{n}\left( {\theta,\phi} \right)}^{H}s_{n}s_{n}^{H}{a_{n}\left( {\theta,\phi} \right)}}{{a_{n}\left( {\theta,\phi} \right)}^{H}{a_{n}\left( {\theta,\phi} \right)}} \right\}}$

FIG. 8 shows a scenario that illustrates one way of combiningdirectional estimation obtained from the array response, with a timedifference measurement. In this scenario the direction between apparatus100 and the two base stations 200 and 300 respectively, has beencalculated from the array response. This means that also the anglebetween those directions can be assessed. However, as illustrated, thisonly narrows down the possible locations 800 at which the apparatus 100may be, since the criteria of those directions and the angle aresatisfied from numerous locations 800 if no direction to a third basestation 400 can be obtained. In the example given in the drawing, acalculated position 810 given from a time difference calculation iscorrelated with the direction estimation. Preferably, an OTDOAmeasurement made by the apparatus on a PRS signal, and reported in ameasurement signal to the network, is used for this purpose. Thiscorrelation may yield a result that the determined location of theapparatus 100 is that of position 820. The illustrated example is basedon the position 810 obtained from the OTDOA calculation is a result ofmeasured time difference from three base stations 200, 300, 400.However, it should be noted that even an OTDOA measurement from only oneor two base stations may be sufficient to improve the positioningobtained from the array response.

In one embodiment, as shown in FIG. 9, the calculation of directionsfrom the array response as described herein, is obtained from signalstransmitted from WLAN access points, 910, 920, e.g. within a building900. Since there may be a lot of reflections within a building, and theexact location of all wireless access points may not be known, thescenario that a sufficiently accurate positioning of the apparatus 100is not possible may occur. In such a scenario it may also be beneficialto correlate the estimated direction to one or more access points 910and/or 920, or a position calculated from such estimated direction, witha position obtained from an OTDOA measurement made on an LTE PRS signal.In the example shown in FIG. 9, an OTDOA measurement carried out inapparatus 100 from a PRS from a base station 400, and reported to thenetwork, provides at least a range of possible distances from that basestations 400. By correlating the direction, or position, data obtainedby the array response from the access points 910 and 920 with thetheoretical trajectory satisfying the distance measurement to the basestation 400, an improved positioning of the apparatus 100 is possible.

FIG. 10 shows another embodiment, in which the geographic position of anapparatus 100 is determined The apparatus 100 may comprise the elementsreferred to with reference to FIG. 1, but for the sake of convenienceonly the motion detector 110 is shown. In this embodiment, the motiondetector 110 comprises an orientation detector, configured to detect therelative orientation of the apparatus 100, with respect to the earth.The motion detector 110 may thus comprise a magnetometer for providingcompass information. Furthermore, the motion detector may comprise oneor more accelerometers, to obtain a reference to the earth'sgravitational direction. So, by means of the motion detector 110, therelative rotational position in space between a local coordinate system(arrows with full lines) and a global reference coordinate system XYZ(arrows with dotted lines) can be determined In the same manner as wasdescribed with reference to FIG. 1, the apparatus 100 is configured toobtain a data set by receiving and sampling a signal from a networktransmitter 200, at different time points while the apparatus 100 ismoved along an arbitrary trajectory. The sampling results in a set ofspatial measurement points, where each measurement point represents atleast the phase of the signal, as sampled at the respective time point.Concurrent with the sampling of the signal, positional data is obtainedfrom the motion detector 110. The positional data indicate the relativeor absolute location of the apparatus 100 in a local coordinate system,for each measurement point m1-m18. Furthermore, the motion detector 110outputs orientation data, regarding the relative rotational positionbetween the local coordinate system and a global coordinate system XYZ.

A measurement signal may thereafter be generated, and transmitted fromthe apparatus 100 to the network, typically to the currently servingbase station or access point. For each transmitted radio signal, themeasurement signal may comprise a plurality of data samples, such asm1-m18, or (m_(1,1), m_(2,1), m_(3,1)) to (m_(1,3), m_(2,3), m_(3,3)),obtained in the apparatus from the respective transmitted signal atdifferent time points during a measurement period with movement. Themeasurement signal may also comprise local position data associated toeach data sample obtained from a local positioning unit in theelectronic device, and orientation data for each point. Alternatively,the position data of the measurement signal is given with referencedirectly to the global coordinate system XYZ. The apparatus 100 isfurther configured to measure distance data from a signal transmittedfrom a network transmitter 200, indicated by the dashed line. Thedistance data may e.g. comprise a timing value, and/or a signal strengthvalue, of the signal received in the apparatus 100. This distance datamay also form part of the measurement signal. Alternatively, thedistance data is transmitted separately from the data samples and theirrespective position data. In an alternative embodiment, the distancedata may be measured by the network transmitter 200, on a signaltransmitted from the apparatus 100, e.g. on a signal transmitted fromthe apparatus 100 in response to a signal received from the networktransmitter 200. The distance data and the position data for the samplesare preferably independent of each other. More specifically, therelative positions for the samples need not take into account thedistance data. In other words: the signal of all data samples are deemedto originate from the same distance to the so as to form a syntheticantenna array. Further processing of the sample data and the distancedata is then preferably performed in the network, such as in a node 500connected to the serving base station, whereby a measurement of thegeographic location of the apparatus may be obtained. A benefit withthis embodiment is that signals from only one network transmitter needto be sampled, for obtaining an estimation of the geographic position ofthe apparatus 100.

In a variant of this embodiment, a directional measurement usingmeasurement data from the apparatus 100 may be used for improvingassessment of its geographic position by the network, when triangulationis not possible. Standard triangulation in a network may be based onestimating the theoretical intersection of measured circles aroundnetwork transmitters, based on propagation time measured to or from anapparatus 100. While three network transmitters are need for completepositioning in space, only signals from (or to) two network transmittersmay be available, or sufficiently direct (along a line of sight) to beuseful. A direction vector of a signal received in the apparatus 100from one network transmitter 200, in accordance with the description ofthe embodiment of FIG. 10, may in such an embodiment be used forcomplementing the lack of signals from (or to) the third networktransmitter.

The invention has mainly been described above with reference to a fewembodiments. However, as is readily appreciated by a person skilled inthe art, other embodiments than the ones disclosed above are equallypossible within the scope and spirit of the invention, which is definedand limited only by the appended patent claims. The benefit ofperforming the direction calculations in the network rather than in theapparatus to be positioned, is that the operator and network does notneed to share the exact location of the base station with the apparatus.Furthermore it is also possible to combine this measurement with othermeasurements that can only be made available in the network to createhybrid location method, e.g. OTDOA measurements or similar that are notnecessarily using angles. The hybrid location method will provide betteraccuracy.

The inventive concept is not limited to mobile phones but could beapplied to any other type of portable electronic device, such as alaptop computer, a palmtop computer, a PDA (Personal Digital Assistant),a tablet computer, a subnotebook computer, a netbook computer, a digitalcamera, a portable media player, a game console, a digital e-bookreader, a digital radio apparatus, or any type of device with a signalreceiving unit, a local positioning unit, and a processor or equivalentmeans for directional estimation and navigational positioning.

1. A method of determining the geographic location of a portableelectronic device in a radio communications network, comprising thesteps of: transmitting radio signals from a first network transmitter,receiving, in the network, a measurement signal from the portableelectronic device, which measurement signal comprises, for thetransmitted radio signal, a plurality of data samples obtained in theelectronic device from the transmitted signal at different time pointsduring a measurement period with movement of the portable electronicdevice, and local position data associated to each data sample obtainedfrom a local positioning unit in the electronic device, so as to form asynthetic antenna array; obtaining, in the network, a directionmeasurement between the electronic device and the first networktransmitter from the synthetic antenna array; obtaining geographiclocation data for the first network transmitter; and identifyinggeographic location data of the portable electronic device based on thedirection measurement and the geographic location data for the firstnetwork transmitter.
 2. The method of claim 1, wherein the step ofdetermining a direction measurement comprises the steps of obtaining anarray response of the synthetic antenna array; and processing thesynthetic antenna array as a function of the array response
 3. Themethod of claim 1, comprising the steps of: obtaining a distancemeasurement, based on a signal received in the apparatus from a secondnetwork transmitter, representing an estimated distance between theapparatus and said second network transmitter.
 4. The method of claim 3,wherein the distance measurement is calculated from time differencedata, received from the portable electronic device, representing timedifference measured between specific signals from a number of networktransmitters.
 5. The method of claim 3, wherein the distance measurementis calculated from propagation time data, measured on a signal betweenthe portable electronic device and the second network transmitter. 6.The method of claim 3, wherein the steps of obtaining a directionmeasurement and obtaining a distance measurement are carried outindependently from each other.
 7. The method of claim 4, wherein thestep of identifying geographic location data comprises the step ofcorrelating geographic location information obtained from processing thesynthetic antenna array, with geographic location information determinedfrom said time difference data.
 8. The method of claim 1, comprising thestep of receiving a relative rotational position of the apparatus withrespect to a global coordinate system, wherein the step of identifyinggeographic location data of the portable electronic device is also basedon said rotational position.
 9. The method of claim 8, wherein saidrelative rotational position is received as compass data from theapparatus.
 10. The method of claim 1, wherein the first networktransmitter is a wireless access points.
 11. The method of claim 1,wherein the first network transmitter is cellular base stations.
 12. Themethod of claim 1, wherein said data samples include signal phase datafor a plurality of physical antenna elements of the apparatus, taken atdifferent time points.
 13. The method of claim 12, wherein the syntheticantenna array comprises one virtual antenna element for each combinationof one of said physical antenna elements and one of said time points.14. The method of claim 2, wherein the array response is a model of atleast the phase of the signal at the local positions as a function ofthe relative location between the synthetic antenna array and thetransmitter.
 15. The method of claim 1, wherein the step of processingthe synthetic antenna array comprises optimizing a function that relatesamplitude and phase of the signal at the local positions to thedirection of arrival of the signal at the synthetic antenna array.
 16. Aportable electronic device, comprising: a signal receiving unitincluding an antenna configured to receive a signal from at least oneremote transmitter; a local positioning unit for determining a localposition of the portable electronic device; and a processor, configuredto obtain a plurality of data samples from the signal at different timepoints during a measurement period with arbitrary movement of theportable electronic device, associate each data sample with a localposition obtained from the local positioning unit so as to form asynthetic antenna array, obtain an array response of the syntheticantenna array, and identify the geographic location of the portableelectronic device, by processing the synthetic antenna array as afunction of the array response and by using knowledge about thegeographic location of the or each remote transmitter, characterized inthat said antenna includes a plurality of antenna elements, wherein theprocessor is configured to obtain a plurality of data samples at eachlocal position of the apparatus.
 17. The portable electronic device ofclaim 16, comprising: a sample timer function, configured to determinethe speed or velocity of movement of the apparatus during themeasurement period, and to control the sample period to target apredetermined distance between the measurement points.